This invention relates to an apparatus for machining the pins of a crankshaft by means of non-rotating tools.
An apparatus of this type has already been disclosed in German Offenlegungsschrift No. 34 40 350, wherein the bearings of a crankshaft are machined by means of honing stones. To machine the crankpins of the crankshaft, honing stones are arranged on two forked levers which can be brought by a bell crank lever mechanism into an opening position and a working position. The forked levers each show a guide shoe on the sides thereof facing the crankpins. In the working position of the forked levers, the crankpin is carried by the guide shoes being pressed against a cylinder jacket surface of the crankpin. The honing stones are disposed in tool carriers each movably carried on a forked lever and able to be pressed by an operating cylinder against the cylinder jacket surface of the crankpin. At machining, the arrangement by which the forked levers are supported must follow the crankpins in their connecting rod-like movements. For this purpose, the crankpins are swingably mounted on a bearing disposed at the machine stand and carry a linear-guided carriage on which the forked levers are guided.
To machine crankshaft pins, it also is known to use machines where the pins are machined by endless sanding belts which are pressed by pressure shoes against the rotating pins. The crankshaft makes a to-and-fro movement in the axial direction. Such apparatus is described by the German Petty Patent No. 86 02 827, according to which the eccentric bearing pins are surrounded by pressure shoes which press an endless sanding belt against part of the surface of the bearing pins. The pressure shoes are mounted on a pair of forked levers which are arranged freely movable so that the pressure shoes follow the movements of the bearing pin during the crankshaft's rotation. Forged crankshafts are particularly suited for such machining.
With the aforementioned apparatuses, the honing stones or the pressure shoes, respectively, are fixed to levers of a fork-type arrangement, which are opened via a bell crank lever mechanism so as to render a change of workpiece possible. As in the case of machining crankshaft pins, all of the pins must simultaneously be machined in one working step. Hence, a number of forked levers and corresponding carriers in which the forked levers are guided, must be provided for, which number corresponds to the number of the pins. Owing to the very crowded construction, above all, of the passenger car crankshafts, there is only insufficient room for the arrangement of the forked levers. For this reason, the forked levers and their bearings must be designed in rather a narrow mode, which leads to an unsatisfactory bending resistance thereof. The bending resistance of the forked levers to be achieved is sufficient as long as only a low pressure must be exerted onto the surfaces of the pins to be machined. This is the case, for example, when smoothing surfaces already ground with which nothing but a minor abrasion of working material is connected. If, however, it is necessary to correct the form of the pins, which renders a higher abrasion of working material and regularly also a stronger pressure of the machining tools necessary, stability of the narrow forked lever mechanism does not suffice. However, a deformation of the forked levers may cause a canting of the grinding tools; that is, the honing stones, and damaging the workpiece.